In such well known electrographic apparatus, a flow of corona ions is modulated by a first electrostatic latent image formed on the photosensitive screen to produce, on a record medium having a layer of dielectric material, a second electrostatic latent image corresponding to an image to be recorded. The photosensitive screen is composed of a mesh-shaped electric conductive substrate coated with an insulating layer, a photosensitive layer, an electric conductive layer, etc. in succession by spraying or by vapor deposition under vacuum. The photosensitive screen used for formation of copies of a manuscript, etc. has meshes whose practical size is preferably 100 to 300 meshes. In order to coat such fine meshes with each of the above mentioned layers, it is extremely efficient to use the vacuum vapor deposition. Substances utilizable for the vacuum vapor deposition are, for example, metals such as Al, Ag, Au, In, etc. and oxides of such metals for the electric conductive layer, Se, Se-Te, Se-As for the photosensitive layer and various kinds of inorganic substance and compounds thereof for the insulating layer. The use of an electric conductive layer formed of metals having a low melting point and an excellent stability and a photosensitive layer formed of Se or Se alloy is of high utility value in practice.
In the case of vapor depositing in vacuum on one side surface of a flat mesh-shaped substrate formed of an etched electric conductive plate, a photosensitive layer and on the opposite side surface thereof an insulating layer and an electric conductive layer in succession to form a photosensitive screen of four layer construction, that portion of the mesh-shaped substrate which is located directly above a vapor supply source becomes regular in cross sectional shape, but each end of the flat mesh-shaped substrate becomes deformed in cross-sectional shape. Since a flow of corona ions is controlled by electric potential applied to each portion of the cross-sectional shape of the mesh-shaped substrate, the deformation in cross-sectional shape of the photosensitive screen results in different mode of modulation of the flow of corona ions. In addition, the deformation in cross-sectional shape of the photosensitive screen exerts adverse influence upon the electric charge on the photosensitive layer and the electric potential attenuation characteristics (brightness attenuation and darkness attenuation) thereof. As a result, the efficient formation of ion current patterns corresponding to optical image could not be attained.